Field of the Invention
The present invention relates to apparatus for electroanesthetizing aquatic animals and, more particularly, to a holding tank for electroanesthetizing fish.
Description of Related Art
Since about the turn of the century, batches of fish have been electroanesthesized for both scientific and commercial purposes. For scientific purposes, small tanks are used to contain a limited number of fish. For commercial purposes, much larger tanks are used to permit electroanesthetizing a large batch of fish commensurate with the production rate of the related commercial purposes. For each purpose, an electric charge is introduced through electrodes disposed at the opposed ends or opposed sides of the tank. A sufficient electrical charge is provided to induce epileptic seizures in the fish. Two significant levels of seizure are recognizable: petit mal and grand mal. In both types of seizures, the fish lose consciousness and lack of motor activity. In petit mal, the muscles of the fish become flaccid but in grand mal, tetany occurs. Normally, the fish recover consciousness almost immediately after the electric charge is removed if the seizure was limited to petit mal. In the event the seizure is grand mal, regaining consciousness is much more gradual.
In both types of seizures, the fish suffer apnea, whether it be a mild or severe loss of breathing. Such loss of breathing has serious consequences for the fish and it is essential that grand mal be avoided. Moreover, petit mal should not be prolonged beyond the minimum time required to maintain unconscious.
Epileptic seizures are always accompanied by severe muscle contractions that are capable of breaking bones and rupturing soft tissues attached to muscle myotomes. These contractions are most commonly of a type known as myoclonic jerks, which are a simultaneous contractions of paired myotomes on either side of the spine. This simultaneous and instantaneous seizure of parallel muscles causes compression fractures of the spine and actually crushing (longitudinally) of individual and groups of vertebrae. Myoclonic jerks have an equal probability of occurrence in both petit mal and grand mal. When electroanesthesia is used for non aquatic animals (it has also been used for humans), it is customary to inject a muscle relaxing drug, such as curare (generally presently banned) or succinyl choline chloride to prevent these damaging muscle contractions from occurring.
More specifically, commercial fish processors of domestically raised fish, such as catfish and trout, use electroanesthesia to stun the fish just prior to processing for market. Typically, this stunning process is crude. A large stainless steel basket filled with hundreds of pounds of fish is hoisted from a holding tank. A steel rod is inserted into and along the central axis of the basket and serves as a first electrode. The basket serves as a second electrode. Electric current is supplied to and flows between the two electrodes and the mass of intervening animal tissues until the fish are completely stunned. Thereafter, the fish are dumped on to moving belts and enter the processing rooms. During application of electric current, the fish suffer myoclonic jerks, have broken backs and bleed internally. This bleeding, appearing in the form of hematomas, are present in the fish fillets sold.
When electroanesthesia is used for the study of various facets of fish, the damage resulting to the tissues and bone structure due to the presently used electroanesthesia procedures prevents certain types of studies and may skew findings or analysis. For fish to be returned to the body of water from where they were taken, such as fish on the endangered list, fatal injuries are unacceptable as well as injuries affecting reproduction, survivability and significant shortening of the life span. Establishing petit mal by introduction of chemicals, including muscle relaxants, is difficult in the case of aquatic animals and is discouraged, if not forbidden, by ecological and environmental considerations.